Telephone system



Feb, 19 1924.

K. S. JOHNSON TELEPHONE SYSTEM Filed Dec. 22 1920 Y W QUE m m n. F- J 9% m. m E f ,0 A a 4 N, f 9% a Patented Feb. 19, 1924.

KENNETH S. JOHNSON, OF JERSEY TRIO COMPANY, INCORPORATED, OF N YORK.

CITY, NEW JERSEY, ASSIGNOE TO WESTERN ELEC- EV] YORK, N. Y., A CORPORATION OF NEW TELEPHONE SYSTEM.

Application filed December 22, 1920. Serial No. 432,522.

To all whom, it may concern:

Be it known that I, KENNETH S. JoHNsoN, a citizen of the United States, residing at Jersey City, in the county of Hudson, State of New Jersey, have invented certain new and useful Improvements in Telephone Sys tems, of which the following is a full, clear, concise, and exactdescription.

This invention relates to telephone systems and in particular to a circuit arrange ment and organization of apparatus employed in a telephone substation.

The object of this invention is to provide a telephone system in which interference between the transmitter and the receiver associated at the same station is reduced to a minimum.

The object of this invention is attained by providing in a telephone substation a neutral receiver (one having a. soft iron core which is only magnetized while current is being supplied to the receiver) and a source of energy connected in series across line conductors, the receiver being furnished with energizing current only when another bridge such as an answering substation is operatively connected acrossthe same conductors,

By properly proportioning the balancing network in an anti-side-tone circuit such as provided in K. S. Johnson Patent No. 1,396,760 of November 15,1921, with particular reference to Fig. 1, it is possible to eliminate side-tone during a conversation. In some circuits. however. an unbalanced condition exists at the calling station until the called party removes his receiver from the switch hook. This unbalance is such as to cause excessive side-tone and at times howling in the receiver especially when the receiver is of the permanent magnet type and mounted in close relation or mechanically coupled withthe transmitter as it is in the case of hand sets and loud speaking telephone sets. By employing a neutral receiver the eliiciency' of which is practically zero until the called party answers and current flows through the receiver winding, objectionable side-tone does not result.

Referring to the accompanying drawing, Fig. 1 represents a telephone circuit emliiodying this invention, Fig. 2 shows a modification of this circuit. Fig. 3 shows diagrammatically a preferred relation of the transformer or electrical coil windings employed. Such a coil forms the subject matter of K. S. Johnson Patent No. 1,426,726, granted August 1, 1922.

Referring in particular to Fig. 1, line conductors 1 and 2 are connected to the terminals 3 and l of the substation A. Also across line conductors 1 and 2 are other substations such as B and C. Between the terminals 3 and 4 connected in series are receiver battery 5, secondary winding 6, primary winding 7, transmitter battery 8, and receiver 9. Connected around primary winding 7 and battery 8 is transmitter. 10 controlled by contact 12 and key 11. Shunting receiver 9 is conductor 16 controlled by key 11 and by contact 13. In parallel with receiver 9 is winding also controlled by key 11 through contact 14.

lVinding 15 comprises resistance of a value to balance the normal impedance of the line when transmitting and thereby to prevent side tone in the receiver. As described in Patent No. 1,396,760, referred to above, the value of this resistance is so chosen with respect to the transformer ratio and the impedance of the line, that energy from the transmitter divides equally between the line and balancing resistance and substantially none of it flows through the receiver. In the above patent, it was assumed that the substation circuit would be connected to lines of fairly uniforn'i and constant impedance. In the system described herein, the lines may be so short that their impedances are materially changed when the distant substation is connected or disconnected from the line. The resistance in winding 15 is given a value to balance the line when the distant substation is connected. It is seen, therefore, that before the distant substation is connected a condition of unbalance is liable to exist and that during this condition the receiver 9 would be sub- 'ject to side tone from the transmitter 10 if the receiver were in operative condition. In accordance with this invention, ahty'pe of receiver is used which is rendered operative only when the circuit is completed by closing the circuit at the distance substation. Thus, at the same time that the receiver is energized, the line assumes its normal lmpedance and thereafter howling-is prevented by reason of the fact that no energy from the transmitter reaches the receiver.

y 11 is h Wo in its normal position llO and in this position conversation may be carried on between such stations as B and C without disturbing station A. lVhen, however, stations A and B, for example, are conversing, key 11 is depressed and switch 17 at station B is closed. The transmitter circuit is then closed through contact 12, that of winding 15 through contact i l and that of receiver 9 through switch 17 at station B. Under these conditions, shunt 16 being open at contact 13, current flows through receiver 9 and energizes it. i i hen stations A and B are conversing a balanced condition exists at station A which has an anti-sidetone circuit and no interference results between transmitter 10 and receiver 9. However, when station A originates a call and the called station such as B has not yet answered, contacts 12and 14 being closed by key 11 and switch 17 being open, an unbalanced condition exists between the receiver and the transmitter favorable to side tone and howling in case a receiver of the permanent magnet type is employed, as a receiver of this type has inherently a high efficiency under the condition of no direct current. In order to prevent interference or side tone during this interval, a neutral type receiver 9 is employed as it has inherently practically zero efliciency when no direct current flows through its windings. Such receiver depends upon an external source of energy to energize it and inasmuch as no direct current flows through thereceiver until connections are completed by another station, such as B, there can be no interference.

lVhat is claimed is:

1. A telephone system comprising, a pair of line conductors; a bridge across said line conductors including a transformer, a neutral receiver and a source of energy in series; a second bridge across said line conductors for completing a circuit through said receiver and source.

2. A telephone system comprising, a transformer having primary, secondary and tertiary windings; a pair of line conductors; a source of energy; a bridge across said line conductors including said primary and secondary windings and said source of energy in series with a neutral receiver and said tertiary winding in parallel with. said receiver; a second bridge across said line for completing the circuit.

3. In a telephone system, an electrical coil comprising primary and secondary closely coupled windings and a tertiary winding loosely coupled to the primary andsecond ary windings; a pair of line conductors; a. bridge across said line conductors including said primary and secondary windings, a source of energy and a neutral receiver in series, a transmitter in shunt across the primary winding and said source, said tertiary winding in parallel with the receiver, and a second bridge across said conductors for completing the receiver circuit.

4. In a telephone system, an electrical coil comprising primary and secondary closely coupled windings and a tertiary winding loosely coupled to the primary and secondary windings; a pair of line conductors; a bridge across said line conductors including a transmitter and a source of energy in parallel, a neutral receiver and a second source of energy in series with said source; a sec- 0nd bridge across said conductors for coinplet-ing a circuit through the receiver.

5. In a telephone system, the combination with line conductors of an anti-side-tone substation comprising a neutral receiver and a source of energy in series therewith bridged across said conductors, and a second bridge across said conductors for completing a circuit through said receiver, said substation comprising a transmitter, and means to prevent signal currents from said transmitter from energizing said receiver when said circuit is completed.

6. A telephone station comprising line terminals, a. neutral receiver, a transmitter, a local source of energy in a path in parallel with the transmitter with respect to said line terminals and a series circuit for said receiver and source adapted to be completed by means external to saidstation.v

7. A telephone station comprising line terminals, a neutral receiver and a transmitter, a source of energy in a path in parallel with said transmitter with respect to said line terminals and in series with said receiver, and external means for completing the circuit through said receiver and source.

8. A telephone station comprisingatrans' mitter, a receiver, a transformer having primal", secondary and tertiary windings and a source of energy; said'receiver, said primary secondary windings and said source connected in series; said transmitter connected in shunt across said primary and said source; and said tertiary winding connected in parallel with the receiver. 7

9. A telephone station comprisinga transmitter, a receiver, a transformer having primary secondary and tertiary windings, a source of energy for said transmitter, a second source of energy for said receiver; the receiver, primary and secondarywindings, said transmitter source and said receiver source connected in series; said transmitter connected in shunt across said pri mary andsaid transmitter source; and said. tertiary winding connected in parallel with said receiver. v

10. In a telephone station comprising a transmitter, a receiver, a transformer coil having closely coupled primar 1 and secondary windings and a tertiary winding loosely coupled to said primary and secondary windings, a source of energy for said receiver; said receiver, said primary and secondary windings, said transmitter source and said receiver source connected in series, said transmitter connected in shunt across said primary and said transmitter source, and said tertiary Winding connected in parallel with the receiver.

11. In a telephone system, the combination with line conductors of a substation comprising a transmitter, a receiver, a transformer having primary, secondary and tertiary windings, and a source of energy; said receiver, said primary and secondary Windings and said source connected in series,

said transmitter connected in shunt across said primary and said source, said tertiary Winding connected in parallel with the receiver, and a bridge across said conductors completing a circuit through said receiver.

12. In a telephone system, the combination with line conductors of a substation comprising, a transmitter, a neutral receiver for preventing side-tone when said conductors are open and means for preventing side-tone when said conductors are closed.

In witness whereof, I hereunto subscribe my name this 17thday of December A. D.,

KENNETH S. JOHNSON. 

